Common Reasons for That Achin' Back

Low back pain is one of the most disabling conditions in the U.S., and experts say that 80 percent of Americans will suffer from it at some point in their lives. It's estimated that back pain costs more than $90 billion a year in lost productivity and work days.

While back pain can be debilitating for many who live with it, in most cases it can be treated non-surgically, according to the National Institute of Neurological Disorders and Stroke. Exercise and staying fit are among the best treatments, back specialists say. Lifting objects using the legs while holding objects away from the body is one of the best ways to prevent it.

There are numerous causes for low back pain, ranging from muscle strains to ordinary daily activities that people don't realize can lead to back problems. ABC News talked to several experts about some of these lesser-known causes of lower back pain.

Obesity

Overweight and obese adults are more likely to have disc degeneration in their lower back than normal-weight adults, according to a new study published in the journal Arthritis & Rheumatism.

Disc degeneration occurs when the discs of the spine start to break down, and it sometimes causes low back pain. While disc degeneration is part of the normal aging process, researchers in China found that among 2,599 Chinese men and women, body mass index (BMI) was significantly higher in people with disc degeneration. They determined the presence of degenerative disc disease using MRIs.

"Our study noted a significant association between the presence, increased extent, and global severity of disc degeneration in overweight and obese adults," wrote the study authors, led by Dino Samartzis, director of orthopedics and traumatology at the University of Hong Kong.

They also found that underweight participants were significantly less likely to have degenerative disc disease.

"When you look at their underweight group compared to other groups, it's a very compelling observation that there's a clear association between weight and disc degeneration," said Dr. Scott Boden, professor of orthopedic surgery and director of the Emory Orthopaedics & Spine Center in Atlanta.

Exactly what that association is, however, is harder to establish.

"It's always been difficult showing obesity is a risk factor for back problems," said Boden. "It's easier to show that people with back problems who are obese are going to have worse symptoms. Being obese will exacerbate symptoms if a back problem already exists."

The authors believe weight gain may cause physical stress on the disc and in addition, chronic inflammation brought on by the fat cells can lead to disc degeneration.

But, as they acknowledged in the study, it's possible that in many cases, pain brought on by disc degeneration led people to be less active, which could have contributed to weight gain, making it difficult to determine whether a cause-and-effect relationship really exists between weight and disc degeneration.

"It does make sense, though, that the more weight is transmitted through your back, the more likely it is to lead to degeneration of the disc," said Dr. Nick Shamie, associate professor of spine surgery at Santa Monica-UCLA Medical Center in Santa Monica, Calif. Shamie was not involved in the study.

The authors say that a better understanding the relationship between body mass index and disc degeneration could spare people from disabling back pain.

"Deeper understanding of how elevated BMI contributes to disc degeneration and low back pain could aid in the development of novel interventions that can improve quality of life for those with these disabling conditions," co-author Dr. Kenneth Cheung, also of the University of Hong Kong, said in a statement.

However, the researchers did not assess pain in any of the study participants, and degenerative disc disease is not always painful.

"It's the result of age-related changes in the spine. Some people get flareups and pain, but most people don't have a lot of problems with it or even know that it's going on," said Boden.

In addition to aging, injuries can cause disc degeneration as well.

Sitting

"Sitting is worse than standing. Sitting for long periods of time puts pressure on your back, especially if you're not using core muscles to support your back," said Shamie.

What's even worse is sitting and leaning forward, which places the maximum amount of force on the lower back, he added.

"The very worst thing is if you're seated and leaning forward to pick something up from the floor. You can pop a disc," he said.

Instead of leaning and reaching, Shamie explained the best way to pick something up is to get on the knees, pick it up and keep the object close to the body.

The National Institute of Neurological Disorders and Stroke recommends sitting in a chair with good lower back support. If sitting for a long time, people should rest their feet on a low stool or stack of books. But if possible, switch sitting positions and get up and walk around a bit throughout the day.

Mattress Type

Whether a soft mattress or a firm mattress is better for the back is up for debate. There hasn't been a lot of research on it, but a 2003 study found that people who slept on medium-firm mattresses reported less back pain.

"If a bed is either too stiff or too soft, it's likely to cause back problems, but there is a lot of individual variation on that," said Dr. Richard Deyo, professor of family medicine at Oregon Health and Sciences University in Portland. "You need enough support so the spine is not sagging, but you don't want it so rigid that the spine is forced into an unnatural position."

High Heels

There's nothing to definitively link wearing high heels to the increased likelihood of developing back pain, but experts say it does make sense.

"Having the heel elevated changes the posture and probably forces the lower back into more of an extended position, and that can be painful over time," said Deyo.

But Shamie said wearing high heels is more likely to affect other parts of the body more than the back.

"High heels can put a lot of stress on your feet, but not as much on your lower back."

Purses and Backpacks

"It makes perfect sense that if you have a heavy backpack, there's definitely a potential risk for injuring your lower back and other joints," said Shamie.

In general, he said, maximum weight should be no more than 10 to 15 percent of body weight.

Deyo, however, said the backpack issue has been controversial, and study findings have been conflicting. Nonetheless, it's probably wise to get an extremely heavy load off the back if possible.

"It's wise to using a rolling suitcase or backpack if you can rather than lifting and twisting. The problem may not be having a load on your back, but lifting and twisting it."

When wearing a backpack, it should be high on the back and close to the body to keep it in the body's center of gravity.

Carrying too much on the shoulder can cause the body to tilt, which could also potentially lead to back problems, Shamie said.